The carotenoid class of substances is classified into two main groups, the carotenes and the xanthophylls. The carotenes, which are pure polyene hydrocarbons such as, for example, β-carotene or lycopene, differ from the xanthophylls which also have oxygen functionalities such as hydroxyl, epoxy and/or carbonyl groups. Typical representatives of the latter group are, inter alia, astaxanthin, canthaxanthin, lutein and zeaxanthin.
The oxygen-containing carotenoids also include citranaxanthin and ethyl β-apo-8′-carotenoate.
Oxygen-containing carotenoids are widespread in nature and occur inter alia in corn (zeaxanthin), in green beans (lutein), in paprika (capsanthin), in egg yolks (lutein) and in shrimps and salmon (astaxanthin), conferring on these foodstuffs their characteristic color.
These polyenes, which can both be obtained by synthesis and be isolated from natural sources, represent important coloring materials and active substances for the human food and animal feed industries and for the pharmaceutical sector and are, as in the case of astaxanthin, active substances with provitamin A activity in salmon.
Both carotenes and xanthophylls are insoluble in water, while the solubility in fats and oils is found to be only low, however. This limited solubility and the great sensitivity to oxidation stand in the way of direct use of the relatively coarse-particled products obtained from chemical synthesis in the coloring of human foods and animal feeds because, in coarsely crystalline form, the substances are not storage-stable and provide only poor coloring results. These effects which are disadvantageous for use of carotenoids in practice are particularly evident in an aqueous medium.
Improved color yields in the direct coloring of human foods can be achieved only by specifically produced formulations in which the active substances are in finely divided form and, if appropriate, protected from oxidation by protective colloids. In addition, use of these formulations in animal feeds leads to a greater bioavailability of the carotenoids or xanthophylls and thus indirectly to improved coloring effects, for example in egg yolk or fish pigmentation.
Various processes have been described for improving the color yields and for increasing the absorbability or bioavailability, and all of them aim at reducing the size of the crystallites of the active substances and bringing the particles to a size in the region below 10 μm.
Numerous methods, inter alia described in Chimia 21, 329 (1967), WO 91/06292 and WO 94/19411, involve the grinding of carotenoids using a colloid mill and thus achieve particle sizes of from 2 to 10 μm.
There also exist a number of combined emulsification/spray drying processes as described, for example, in DE-A-12 11 911 or in EP-A-0 410 236.
According to European patent EP-B-0 065 193, carotenoid products in finely divided powder form are produced by dissolving a carotenoid in a volatile, water-miscible organic solvent at elevated temperatures, if appropriate under elevated pressure, and precipitating the carotenoid by mixing with an aqueous solution of a protective colloid and then spray drying.
An analogous process for producing carotenoid products in finely divided powder form is described in EP-A-0 937 412 with use of water-immiscible solvents.
DE-A-44 24 085 describes the use of partially degraded soybean proteins as protective colloids for lipid-soluble active substances. The soybean proteins disclosed herein have a degree of degradation of from 0.1 to 5%.
DE-A-101 04 494 describes the production of carotenoid dry powders by use of soybean proteins together with lactose as protective colloids.
Despite the carotenoid formulations already numerously described in the prior art mentioned at the outset, there continues to be a need for improvements in these preparations, whether in relation to an increased bioavailability or, in particular, in relation to a better storage stability, for example in tablets.